Hitherto, image fixing methods of a printing substrate in a printer using electrophotography have included a heat roller fixing method in which a printing paper is passed through heat rollers internally equipped with a motor lamp to pressurize a toner on the printing paper and an oven fixing method in which a printing paper is passed through an oven heated by infrared radiation. In these fixing methods, however, in cases where a printing paper is jammed in a fixing portion, there have been disadvantages in that a trace of pressure remains on the printing paper and the danger of fire is caused by high temperature heating.
Recently, to solve these disadvantages, a photofixing method, represented by a flash fixing method, has been put into practical use in a printer which may be used automatically for a long period of time, for instance, in output of computers. The flash fixing method is a method in which the fixation is conducted by a flash of a discharge tube such as xenon flash lamp and which flash fixing method is characterized in (1) less resolving degree deterioration on fixing due to non-contact fixation, (2) relatively short warm-up time, (3) less danger of fire on a printing paper jamming, and (4) fixing being possible almost irrespectively of the thickness and the kind of materials of a printing paper. In the flash fixing method, however, without controlling the irradiation period and method and the amount of a flash energy for a toner image and the heat decomposability and viscoelasticity of a toner, a bursting-like blank area, called "void phenomenon", is partly formed in a fixed image, whereby the image quality of a printed paper is deteriorated.
In order to prevent the "void phenomenon", JP-A-Hei-2-22668 proposes a toner to which an inorganic filler is added, JP-A-Hei-l-234857 proposes a toner containing a polyolefin wax, JP-A-Hei-4-328576 proposes a toner to which a thermoplastic resin grain is added, JP-A-Sho-59-129862 proposes mixing of an epoxy resin with a styrene/acrylic resin, and JP-A-Hei-4-250464 proposes mixing of an epoxy resin with a crystalline polyester. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) However, these approaches have still not provided satisfactory improved effects. In particular, there have been not provided any examples in which a styrene type resin is used as a main component for a binder resin.